Mineral flotation



Patented July 7, 1953 H. Hill, Pittsburgh, Pa., assignors to Koppers Company, 1110., Pittsburgh, Pa., a corporation of Delaware No Drawing. Application July 6, 1949, Serial No. 10.3,314.

9 Claims.

This invention relates to mineral flotation. More particularly the invention relates to the concentration of minerals in sulfide ores with a Z-mercaptobenzimidazole flotation collector.

A primary object of the invention is to provide new flotation reagents.

A further object of. the invention is to provide. new and effective collectors for the flotation of sulfide ores.

A still further object is to provide new 001- lectors for the flotation of sulfide ores which are especially effective in floating zinc, lead and copper sulfides.

A still further object of the invention is to provide new collectors for the selective flotation of zinc sulfide in the recovery of zinc sulfide fromv lead tails.

It has been proposed heretofore to utilize 2- thio 4,4,5,5, tetramethyltetrahydroimidazole, which has the structure as. a. collector in the flotation of copper sulfide. See for example U. S. Patent 1,801,319 granted April 21, 1931 to Moses, Hess and Perkins. In spite of this disclosure, flotation agents of this type have not found favor in industry. It has been found, however, that compounds containing eneimidazoles are effective for the flotation of copper sulfide, markedly more so than the thiotetrahydroimidazole of the prior art, and, what is even more surprising, that these same compounds are unusually effective for the flotation of zinc sulfides. We have found also that these same compounds are effectiveforthe'flotati'on of lead sulfides. The Z-mercapto-imidazoles which are useful in floating sulfide ores according to the invention are compounds containing not more than twelve carbon atoms which have an aromatic ring fused with an imidazole ring and which are free of hydrophilic, or water solubilizing substituents other than the mercapto group. The compounds may be referred to generically as Z-mercapto- 4,5-aryleneimidazoles which arefree of hydrophilic substituents and contain not more than twelve carbon atoms.

The 2-mercapto-4,5-aryleneimidazoles useful. in the processes of the invention are well known in the art and may be prepared in any suitable manner as, for example, from carbon disulfide and ortho arylenediamines. Suitable compounds,'for example, may be prepared by the interaction of carbon disulfide or thiophosgene I with ortho-phenylenediamine and 1,2-naphthy1- the thiotetrahydroimidazole ring structure are not useful in selective flotation of zinc sulfide in lead-zinc sulfide ores. The simplest of this series, namely ethylene thiourea, which has the of the prior art are avoided by effecting the' flotation in the presence of certain mercaptoimidazoles as distinguished from. the mercaptohydroimidazoles of the prior art. We have found for example that certain 2-mercapto-4,5-arylenediamine as Well as the homologues thereof, such as 3,4ediaminotoluene, and other alkyl derivatives thereof. By suitable choice of reagents, it is, possible to produce 2-mercaptobenzimidazoles having one or. more of the nuclear hydrogen atoms replaced by an alkyl radical, or radicals, 'having less than a total of. six carbon atoms; Z-mercaptobenzimidazoles having one or more of the nuclear C-hydro'gen atoms replaced by an alkoxy radical, or radicals, havingrless than a total of six carbon atoms; 2- mercaptobenzimidazoles containing a methyl group attached to either the carbocyclic, ring or heterocyclic ring and Z-mercaptonaphthimidazoles containing a methoxy group attached to the carbocyclic ring. Suitable substituent groups include methyl, ethyl, .n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, mixed amyl, t-amyl and the corresponding alkoxy radicals. (Lellmann, Liebig s Annelen der Chemie, 221, pages 9,. and 10; Billester, Steiner, Ber. der Deutschen Chemischen Gesellschaft,20-, pages 229 to 23.1; Kyn. Journal fiir Praktische Chemie, (2), 75, page 324).

The collectors of the invention are difiicultly soluble in water and soluble in alkaline solutions. They may be introduced into the flotation circuit as such or in solution in alkaline solutions or as their water soluble salts, such as the sodium, potassium, or other alkali metal salt. When the ucts.

3. material is introduced as such, i. e., without so ubilizing alkali, it is desirable that it be conditioned by fine grinding to micron size with or sulfonates, particularly the alkyl benzene sulfonates, and such non-ionic wetting agents as the polyether and polyester condensation prod with solid alkalies, such as sodium carbonate and lime, to provide a material which can be applied more readily by the mill operator.

In carrying out froth flotation in accordance With the invention, a 2-mercapto-4,5-aryleneimidazole which is free of hydrophilic substituents and contains less than twelve carbon atoms is incorporated into the mineral pulp in any suitable manner according to the practices of this particular art and the thus prepared mineral pulp subjected to froth flotation in any suitable apparatus according to the various practices well understood by those skilled in the art. The reagents, for example, may be added to the grinding mills in the preparation of the mineral pulp, or they may be added to the ground pulp in suitable conditioners, or they may be added directly to the flotation cells. However, introduced or incorporated in the mineral pulp, the reagents of the invention are effective in very small quantities. To effect the processes of the invention therefore it is only necessary to in corporate in the mineral pulp a small amount of the collector. Actually less than one pound of these novel collectors per ton of ore to be treated suflices and, in most cases, as little as one-tenth of a pound or less is satisfactory.

It is to be understood that various conditioning agents ma be incorporated in the various flotation circuits according to the practices Well understood and common in the art. Thus, agents adapted to adjust the pH of the circuit may be'introduced. Lime and sodium carbonate, for example, are commonly employed to adjust the alkalinity as required to give the best selective flotation. Similarly, frothers and other conditioners may be added as required to produce a desirable froth. Depressors and activators also may be added as required. Sodium cyanide and zinc sulfate, for eXample,'may be incorporated in a leadcircuit to act as depressors for zinc, while copper sulfate may be added to the lead tail in a zinc circuit to activate the zinc.

' E AMPLE 1 A lead tail containing 6.70% zinc was subjected to froth flotation using Z-mercaptobenzimidazole as the collector. The zinc rougher concentrate contained 41.41% zinc and ac-. counted for about 97.5% of the zinc contained in the lead tail. The zinc tail contained 0.17% zinc or about 2.5% of the zinc contained in the lead tail. The Z-mercaptobenzimidazole, therefore, gave a 97.5% recovery of the zinc of the lead tail.

The lead tail was obtained by subjecting a 14% lead, 6% zinc lead-zinc sulfide ore, to froth flotation in a lead circuit as follows: The ore was The collectors may also be compounded ground at solids so that 3.8% remained on a 100 mesh screen and 51.3% passed through a 200 mesh screen, and conditioned wi'th 0.2 pound of sodium cyanide, 1.0 pound zinc sulfate, 0.04 pound Minerec B (MinerecfB is a trade-name fora collector obtained" by reacting .xanthate,

sodium or potassium butyl Xanthate, with' ethyl chlorocarbonate) and 0.01 pound of Z3 (potassium ethyl xanthate) per ton of ore. The mineral pulp, adjusted to a density of 25% solids, and an alkalinity of pH 7.7, was then subjected to a 4-minute float, to float off the lead con centrate. r

The zinc float was 'efiected after neutralizing the zinc depressors (sodium cyanide and zinc ,sulfat'e) with 0.75 pound per ton of copper sulfate, adjusting the alkalinity to pH 9.8 with 2.25 pounds per ton of lime and adding 0.01 pound per ton Z-meroaptobenzimidazole added in the form of an aqueous solution prepared by dissolving 0.5 part of 2-mercaptobenzimidazole in a sodium'hydroxide solution containing 1 part sodium hydroxide in 10 volume .parts of water and thereafter diluting to 100 volume parts.

It will be seen from these data that 2-mercaptobenzimidazole is an effective zinc collector giv ing excellent recovery of the zinc, 97.5%,,and an unusually high rougher concentrate, 41.41%

If desired, the Z-mercaptobenzimidazole can be used as the collector in the lead circuit, though generally speaking this is less desirable because its high efficiency, as a' zinc collector tends to cause it to pull too much zinc in the lead circuit thereby tending to reduce the over all recovery of the zinc from the ores. Thus, when 0.05 pound per ton of Z-mercaptobenzimidazole was used in place of the MinerecB and the Z3, along with 0.04 pound of 'pine oil per ton of ore as a frother, a lead rougher concentrate, containing 60.2% lead and accounting for 93% of the total lead in the ore, was obtained. The lead tail contained 1.29% lead or 7% of the total lead of the ore. It is believed, however, that the lead content of the tail can be lowered and the lead recovery improved by suitable adjustment of conditions, particularly with regard to the amount of zinc depressors and the amount of Z-mercaptobenzimidazole.

A further indication of the effectiveness of 2- mercaptobenzimidazole in floating zinc sulfide is given in the following example.

EXAMPLE 2 I A lead tail containing about 3% zinc was subjected to froth flotation, as described in Example 1, using Z-mercaptobenzirhidazole as the collector. ,Comparison runs were made with 3-140 (a thiopyrimidine obtained by the condensation of mesityl oxide and ammonium thiocyanate) and ethylene .thiourea.

The'comparative results are shown in the following table.

From these data it will be 'seen that for this Q particular-"ore 2-mercaptobenziniidazole is somewhat.- more effective as a zinc collector'than' the standard 'B140,-Whichis one of the most effeccopper sulfide ores.

6 in'g these tests, but they are both described. as

The. preferred form (if-the invention been thusfidescribedjwhat. is claimed as new is:

tive zinc collectors known. It will be noted par- 5 We claim: ticularlythat with ethylene thiourea as. a col-. 1. In a process for the froth flotation' ofafsul; lector, more of the total zinc was left inthe' tail fidic ore the, sten'of efiecting thefiotation in the than was collected: in the concentrate, while with presence of Z-mercaptobenzimidazole. Z-mercaptobenzimidazole, up to 15 times as much 2. A. method of concentrating minerals of 'sul zine wasrecovered in the concentrate aswas 10st 10 fide ores compris ngp ep lting. a mineral pulp of in'the tail. said ore, incorporating therein a small amount The leadtail used in the above test was obof 2-mercaptobenzimi'daz ole' and subjecting the tained using the procedure described in Example mixture to frothflotation.

l with a lead-zinc ore analyzing about 9.5% lead 3. The method defined in claim 2 in which the and about 3.1% zinc. This ore was ground to 2-mercapto-4,5-aryleneimidazole is conditioned a fineness such that 3.5% remained on a 65 mesh by fine grinding to micron size with a wetting screen, 7.8% on a 100 mesh screen, 23.2% on a agent to assist its incorporation in the mineral, 200 mesh screen, and 65.5% passed through a 200 pulp in the flotation cell.

mesh screen. The lead float was made with 1.0 v 4. A method of concentrating zinc sulfide in pound zinc sulfate, 0.20 pound sodium cyanide, sulfid r s mpr si g p par a n al p p 0.04 ound Minerec B, 0.01 pound Z3, and 0.04 Of said ore, incorporating t er n asmall amount pound pine oil, whereas the lead tail'used'in the of 2-mercapto nz mida l and su j t e zinc float was conditioned with 0.04 pound pine mixture to froth flotation.

oil, 2.25 pounds lime, 0.75 pound copper sulfate, 5. A method of concentrating lead sulfide in and the indicated proportion of collector. sulfide ores comp i g preparing a mineral pulp The utility of the collectors of the invention Of said ore, incorp ratin therein a Small amount in floating copper sulfide is illustrated in the folf 2-mercapt0benzimidazole and subjectin the lowing example. mixture to froth flotation.

' 6. A method fOr preparing a concentrate of a EXAMPLE 3 copper sulfide ore which comprises preparing A 3.4% copper ore was 'ball milled with 4.5 a mineral'pulp of said ore incorporating therein pounds per ton of lime, and part of the collector a small amount of Z-mercaptobenzimidazole and was added, and the pulp at 25% solid was consubjecting the mixture to froth flotation. ditioned for one minute. 0.04 pound of a mix- 7. A method of concentratingzinc sulfide in ture of Pentasol (mixed amyl alcohols) and pine a tail obtainedin the froth flotation of lead suloil was added, and the copper floated for 3 fide from a lead-zinc sulfide ore comprising preminutes. Thereafter, another part of the colparing a mineral pulp of said tail neutralizing lector and a further quantity of 0.04 pound zinc depressor therein and'incorporating therein Pentasol and pine oil mixture was added and a small amount of Z-mercaptobenzimidazol and the pulp conditioned for 1 minute. A second 40 subject ng the mixture to froth flotation. float was then carried out for 4 minutes. Com- 8. In a method of separating lead and zinc parison runs were made between z-mercaptosulfides in sulfidic ores by means of froth flotation benzimidazole and B-l40, one of the more eiTecin which a mineral pulp s fi Subjected to froth tive copper collectors. flotation to float the lead sulfide and leave a lead The results obtained are given in the following tail containing the bulk of the zinc sulfide and table, then the lead tail subjected to a. second froth Table II Concentrate Middllngs Tail Percent Lbs./ Recovery Collector Ton Percent Percent Percent Percent Percent Percent g Cu Recovery Cu Recovery Cu Loss opper 0.01 2-mercaptobenzlmldazole. O-JBI 25.55 69.3 7.74 26.6 0.8 4.1 95.9

It is significant to note from the data given in flotation to carry off a zinc concentrate and leave this table that z-mercaptobenzimidazole is subthe zinc tail containing the bulk of the gangue, stantially as effective as the standard thiothe improvement which comprises efiecting said pyrimidine, the total recovery in all three cases 5 froth flotation of said lead tail in the presence ranging from 96% to 98%. of Z-mercaDtobenzimidazole.

It is interesting .to compare the data of Table 9. Amethod of concentrating-minerals of sul- II with the data given in the patent to Moses fide ores containing lead and zinc sulfides com-' 1,801,319 where twenty-five times as much thioprising prep ring a mineral pulp. incorp ra in tetrahydroimidazole collecting agent is used as therein alead collector together with a zinc dethe Z-mercaptobenzimidazole collecting agent as M 8 and subjecting e xtu e to froth flotashown in Table II.v The Moses et al. recovery tion to carryoffa lead concentrate and to leave is 7 37 7;, of copper as compared t 93% copper a lead tail containing zinc,then incorporating a recovery it t present invention, t being zinc activator together with a small amount of understood that different ores were used in male- Z-mBICaDtObBH-ZimidaZOIB d subjectin the havin 7 7 mixture tofroth-fiotation to 'recover a zinc con Number i? Name" I f Date;- centrate. 1,801,319 l 'Moses'et 21; Apr. 21,1931 '5 ii "THOMAS E. ROBBINS;-JRL 1,806,362 Moses et a1. May 19, .1931

' WILLIAM. H. 1,852,107-

Chri'stmanmet. a1. ;'Apr. 5; 1932 I 5 -2,297,664 *Tartaronet a1.1 Sept-29, 1942 V References Cited in the file of this patent 2,3 4,272 c t 1; 1 B 5, .1944 NIT PATENTS 2,3801398 Jayne,-Jr July 31, 1945 Number Name Date FOREIGN T NT v V 7 [Bolton Oct. 28. 10 Numb er I QQ Q 7 Moses -----'---A 21, 3 617,944 Great Britain' Feb. 14,1949 

1. IN A PROCESS FOR THE FROTH FLOTATION OF A SULFIDIC ORE THE STEP OF EFFECTING THE FLOTATION IN THE PRESENCE OF 2-MERCAPTOBENZIMIDAZOLE. 